It sounds like your boa is way to small for his age. My adult male eats XL rats every two weeks and my adult female, XXXL rats. You should first try converting him over to frozen / thawed, since you will eventually be feeding him much larger meals. An every ten day diet is perfect for his size, but you will need to feed him larger meals to get some weight on him. I bet with a good feeding regimen he will grow longer and put on a lot of weight. You need to feed him prey that is just a little larger than the thickest part of his body. Although you do now want to the prey to be too large, you want to see a lump after he swallows the meal. This is pretty easily accomplished when feeding frozen thawed. Keep increasing the size of the rodents until he is has some good weight to him, and then start feeding him every fourteen days. It is very easy to feed them too much, and you do not want him to become obese. Obesity in boas can be very dangerous for their health, and overfeeding has killed many boas. Good luck, and I hope this helps.